Especially in conveying systems operating with automatic control, such as in elevator systems, there must be a safety system according to safety regulations, by the aid of which safety system the operation of the conveying system can be stopped e.g. as a consequence of a defect or of an operating error. The aforementioned safety system comprises safety switches, which measure the safety of the system. When detecting that the safety of the conveying system has been endangered, the operation of the conveying system is interrupted and the conveying system is brought into a safe state by controlling the safety system.
Elevator regulations require that an elevator comprises safety switches, which are configured to measure functions that are critical from the viewpoint of the safety of the elevator system. Consequently, the elevator must comprise an extreme limit switch, which limits the extreme limit of the permitted movement of the elevator car in the elevator hoistway. A safety arrangement of an elevator also comprises an end buffer, the task of which is to damp the impact caused by collision of the elevator car with the end of the elevator hoistway. The extreme limit switch changes its state when the elevator car arrives at the extreme limit for permitted movement of the elevator car, said extreme limit being monitored by the extreme limit switch. The safety regulations require that the elevator car is stopped when the elevator car arrives at the extreme limit switch. The safety regulations also require that the end buffer stops movement of the elevator car before collision with the end of the elevator hoistway.
An extreme limit switch is conventionally implemented with a limit switch installed on the roof of the elevator car, which limit switch fulfills the requirements of a safety contact. Metal ramps are installed in the top end and in the bottom end of the elevator hoistway. When the elevator car passes an end floor, the ramp pushes the lever arm of the extreme limit switch, which then rotates and opens the contacts of the extreme limit switch.
It is important to ensure that the elevator cannot be taken into use without functioning and testable safety devices that comply with the regulations. However, testing of an extreme limit switch, i.e. manual measurement of the operating point of the extreme limit switch as well as of the air gap of the opened contact, is awkward. The elevator cannot from the elevator hoistway be driven with the service drive apparatus to the extreme limit switch, because according to the regulations the elevator must be stopped and remain jammed when it reaches the extreme limit switch on service drive. For this reason, conventionally it has been endeavored to position the elevator at the point of the extreme limit switch for testing by driving the elevator manually with the emergency drive apparatus from outside the elevator hoistway. Manual positioning of the elevator at the extreme limit switch by the aid of the emergency drive apparatus is, however, difficult because, firstly, the serviceman driving the elevator does not have direct visual contact into the elevator hoistway and, secondly, the stopping area at the point of the extreme limit switch is quite narrow and finding the correct stopping point generally requires several attempts.
If the operating point of the extreme limit switch comes too close to the terminal floor, the elevator car might remain jammed when it arrives at the terminal floor, in which case operation of the elevator ceases in accordance with the safety regulations and the return of the elevator to normal operation requires a serviceman to pay a visit to the site of the elevator and perform the necessary procedures.
If the operating point of the extreme limit switch comes too far from the terminal floor, the extreme limit switch does not necessarily function after the elevator rope has stretched slightly. In this case the counterweight might collide with the end buffer before the extreme limit switch stops the elevator.
Consequently there is a need to develop the testing of the operation of safety devices, such as of extreme limit switches.